1. Technical Field
This invention relates to pressure compensating bases for polymeric containers used in hot fill, pasteurization, and retort applications.
2. Background Art
Blow molding processes for forming polymeric containers are well known in the art. Blown polymeric containers have replaced metal and glass containers in numerous food storage applications such as carbonated soft drinks and lower temperature filled food products such as peanut butter and mayonnaise. However, certain prior art containers such as polyethylene terephthalate (“PET”) containers have not replaced metal and glass containers for product storage and processing applications where the container is filled or heated to temperatures above 97° C. (207° F.) as such containers experience significant shrinkage deformation rendering the container unusable.
Additional in-roads into the replacement of glass are desired in food processing applications such as low-temperature pasteurization, high-temperature pasteurization, and retort. Low temperature pasteurization includes the pasteurization of liquid products such as beer and tea. High temperature pasteurization processes are for solid food products such as pickles that have slower heat transfer rates and require temperatures in excess of 100° C. (212° F.). Retort processes are for pasteurizing low acid products and require temperatures from 100° C. to 130° C. (212° F. to 266° F.) and pressures sufficient to maintain water in a liquid state.
In numerous food storage applications, polymeric containers are filled with a hot liquid or solid material, the container is capped and then allowed to cool. To compensate for the change in volume inside the container it is known to provide pressure compensating features in various locations on the container sidewall including the dome, the barrel, and the bottom panel. The pressure compensating features move in response to pressure changes to decrease or increase the volume as needed. United States Publication Nos. 2009/0202766 and 2009/0159556 and U.S. Pat. Nos. 7,451,886; 7,150,372; 6,942,116; and 6,595,380 disclose a volume compensating feature on a bottom panel of the container having a centrally disposed, generally inverted, cone shaped, push-up section that extends to an axially inwardly most point when compared to other portions of the bottom panel. The push up section is connected by a generally S-shaped panel to a standing ring. The S-shaped panel inverts to compensate for negative pressure in the container. The '556 publication further discloses providing a plurality of axially spaced, circumferentially extending grooves on the S-shaped panel that extend through the entire thickness of the wall and form ribs on an opposite side of the groove or a plurality of circumferentially and axially spaced dimples. The bottom panels are symmetrically disposed about an axis of the container.
U.S. Pat. Nos. 6,983,858; 6,857,531; and 5,234,126 disclose a pressure compensating base for a polymeric container that under static pressure the bottom panel is convex, or extends axially outwardly, and snaps through to a concave configuration, or extends axially inwardly, when a specific pressure is reached within the container.
United States Patent Application Publication No. 2006/0231985 discloses a method and apparatus for manufacturing a blow molded container. A parison is mounted within a mold assembly having two side molds and a base mold. The parison is inflated in contact with surfaces of the mold assembly to form a container with a bottom wall having a moveable region. The moveable region is downwardly convex with respect to a bearing surface and has a centrally disposed dimple. After the inflation step is complete, a rod mounted within the base mold for reciprocating translational motion along an axis of the container is moved axially inwardly so that a rod end engages the dimple of the moveable region to reposition the moveable region axially inwardly to an interior portion of the container with respect to the bearing surface.
United States Patent Publication No. 2008/0047964 discloses a plastic container having an invertible base for pressure compensation. A pressure panel is deeply set into the container and is moveable between an outwardly inclined position to an inwardly inclined position to reduce the internal volume of the container and to compensate for vacuum forces created during a hot-fill process. The pressure panel is connected to the standing ring by an inner wall that is parallel or nearly parallel to a longitudinal axis of the container. To facilitate movement of the pressure panel between the outwardly inclined position to the inwardly inclined position, the pressure panel can include a hinge structure that is located between the inner wall and the pressure panel. The pressure panel can have an initiator portion and a control portion where the control portion has a steeper angle with respect to a standing plane than the initiator portion. The '964 application further discloses a pressure panel divided into fluted regions to create regions of lesser and greater angular inclination.
To overcome the shortcomings of known containers, a new plastic container having pressure compensating features is provided. The container may have a pressure compensating base capable of progressively yielding under pressure. The pressure compensating base of the present invention will allow for all other surfaces of the container to be free of pressure compensating features. These and other aspects and attributes of the present invention will be discussed with reference to the following drawings and accompanying specification.